1. Technical Field of the Invention
The present invention relates to a device for protecting against electrostatic discharges to a capacitor placed in series at the input of an electric circuit. More particularly, the present invention relates to such a protection device for a circuit forming part of an electrical device having electronic components distributed over two supports.
2. Description of Related Art
It is common to use a capacitor connected in series at certain inputs of electric circuits, in particular to remove any D.C. components from the electrical signal applied to this input. Such a capacitor, called a series capacitor, is then inserted between an input terminal of said electric circuit and an external connection terminal.
Depending on their location within an electrical device, some connection terminals are susceptible to receiving electrostatic discharges. Electrostatic discharges may especially occur when the electrical device is handled by an operator. They may cause instantaneous voltages greater than 2000 volts, capable of damaging some components of the electrical device. It is therefore usual to connect a connection terminal to a device protecting against electrostatic discharges, or an ESD protection device.
The principle of an ESD protection device consists in opening a path for removing electrical charges between the connection terminal to which the ESD protection device is connected and a reference point in the electric circuit when the voltage between said connection terminal and this reference point exceeds a predefined threshold. In normal operation, an ESD protection device has no electrical effect, then being equivalent to an open circuit, but it limits the voltage between the connection terminal and the reference point in the presence of an electrostatic discharge. Such an ESD protection device is hereinafter called a voltage limiter.
For an input terminal of an electric circuit connected to an external connection terminal by a series capacitor, the connection of said external connection terminal to an ESD protection device makes it possible to prevent an electrostatic discharge occurring on the external connection terminal from causing breakdown of the series capacitor.
Now some electrical devices have several supports over which the electronic components of these devices are distributed. In particular, an external connection terminal connected to a series capacitor, as introduced above, may be borne by a support which does not itself bear ESD protection. In particular, this may be the case when the support for the external connection terminal is an insulator.
There exists a need for protecting a series capacitor connected to an external connection terminal against electrostatic discharges occurring on said external connection terminal with respect to electrical devices having several supports for electronic components.